Occurrence of NDM-1-producing Morganella morganii and Proteus mirabilis in a single patient in Portugal: Probable in vivo transfer by conjugation

Objectives: To decipher the genetics of acquisition of carbapenemase-encoding genes identified in two carbapenem-resistant Enterobacteriaceae recovered from a single patient in Portugal. Methods: Carbapenemase genes were searched by PCR assays and mating-out assays were performed to further characterize the plasmid support of the carbapenemase genes. Genetic characterization of the plasmid supports was performed by whole-plasmid sequencing using the Illumina technology. Results: We identified here two NDM-1-producing isolates, namely a Morganella morganii and a Proteus mirabilis, sharing the same bla_NDM-1-positive plasmid. This 154 kb plasmid belonged to the IncA/C₂ type, recently renamed IncC, and co-harboured two AmpC β-lactamase genes, namely bla_CMY-4 and bla_DHA-1, in addition to the 16S rRNA methylase gene armA encoding high-level resistance to aminoglycosides. In addition, the M. morganii isolate produced the CTX-M-33 extended-spectrum β-lactamase possessing weak carbapenemase activity, encoded by another plasmid. Conclusions: We showed here that, in addition to KPC-type and OXA-181 carbapenemases, which have been identified as widespread in this country, another concern is the emergence of NDM-1-producing enterobacterial isolates in Portugal. We demonstrated here the in vivo plasmid transfer of a bla_NDM-1-positive plasmid leading to dissemination of this carbapenemase gene within different enterobacterial species in a single patient.